Medical tubes include tubes for introducing or withdrawing substances into or from a body, and catheters inserted into a body for examination or treatment. Specific examples of the medical tubes include catheters such as urinary catheters, stomach catheters and suction catheters; tubes such as infusion tubes, enteral feeding tubes, peritoneal dialysis tubes, blood transfusion tubes and tubes connected to urinary catheters to guide urine to urine collection bags; circuit tubes used in blood circuits for hemodialysis, artificial heart-lung machines and plasmapheresis; and tubes for transporting substances in the medical field. The transporting tubes for medical substances include tubes attached to multiple blood bags and tubes for connecting an aspirator and a catheter. Many of the conventional medical tubes are made of polyvinyl chloride that is inexpensive and possesses excellent kink resistance and a certain level of flexibility (pliancy). However, alternative materials have been required because of environmental concerns.
The alternatives studied so far include styrene elastomer compositions (JP-A-2000-63577, JP-A-2001-252348 and JP-A-2001-1432), thermoplastic polyurethane compositions (JP-A-H05-84293 and JP-A-2001-46492), and syndiotactic 1,2-polybutadiene compositions (JP-A-2000-334038 and JP-A-2001-104473). The fact, however, is that these compositions have low versatility and practical utility due to insufficient flexibility and high costs. (Patent Documents 1-7)
To achieve the versatility and practical utility, studies have been made on copolymers of ethylene and α-olefins of 3 or more carbon atoms, and acid copolymers of ethylene and vinyl acetate or the like. However, none has satisfied performances required such as flexibility, heat resistance and kink resistance.
Meanwhile, polypropylenes include isotactic polypropylenes and syndiotactic polypropylenes. Particularly, the isotactic polypropylenes are inexpensive and excellent in transparency and heat resistance, and are therefore widely used in various packaging materials and industrial materials. However, their flexibility is unsatisfactory. To solve this problem, compositions have been studied in which flexible materials such as ethylene elastomers are blended with the polypropylenes. However, none has satisfied performances required. Medical tubes of syndiotactic polypropylene resin compositions have recently been proposed (WO 2004/067627), but their heat resistance and breaking strength have been insufficient. (Patent Document 8)    [Patent Document 1] JP-A-2000-63577    [Patent Document 2] JP-A-2001-252348    [Patent Document 3] JP-A-2001-1432    [Patent Document 4] JP-A-H05-84293    [Patent Document 5] JP-A-2001-46492    [Patent Document 6] JP-A-2000-334038    [Patent Document 7] JP-A-2001-104473    [Patent Document 8] WO 2004/067627